This invention relates to a display device comprising an electro-optical medium between two supporting plates and provided with a system of pixels arranged in rows and columns. The display device includes means for providing row and column connections with selection and data voltages wherein the column connections are provided with column voltages during at least a part of a selection period in which the rows are selected via drive elements.
More generally, the invention relates to a display device comprising at least one pixel with an electro-optical medium between picture electrodes defining the pixel and a drive unit for applying drive voltages to the electrodes.
The invention also relates to a method of manufacturing a display device comprising a system of pixels with an electro-optical medium between electrodes defining pixels and a drive unit for applying drive voltages to the electrodes.
The invention also relates to a device for adjusting such a drive unit.
A display device of this type is suitable for displaying alpha-numerical information and video information by means of passive electro-optical display media such as, for example, liquid crystals, electrophoretic suspensions and electrochromic materials.
A display device of the type described in the opening paragraph is known from Netherlands publication no. 8701420 which corresponds to U.S. Pat. No. 5,032,831 (Jul. 16, 1991) in the name of K. E. Kuijk. In a display device shown in this publication the pixels are given a defined value for each row because the capacitances associated with these pixels are accurately charged or discharged after they have been discharged or charged too far (either accurately or not) To this end such a picture display device is provided with means for applying, prior to selection, an auxiliary voltage across the pixels, which voltage is beyond or on the edge of the voltage range to be used for picture display.
In other display devices the pixels are driven via MIMs or thin-film transistors whose gate electrodes are connected to selection rows and whose source electrodes are connected to data rows.
Notably in liquid crystal display devices the capacitance associated with a pixel may vary with the applied drive voltage and this may detrimentally influence the response time. This influence can be easily demonstrated by way of an example.
A display element or picture cell (pixel) has, for example, a capacitance C.sub.I at a drive voltage V.sub.I. When the pixel is driven with a voltage V.sub.J in an address or selection period, the total charge on the pixel will be C.sub.I V.sub.J, while the pixel will tend to adjust itself to the capacitance C.sub.J associated with the voltage V.sub.J, inter alia, because the liquid crystal material is oriented differently. Due to charge preservation the voltage and the capacitance of the pixel will settle at values V.sub.K and C.sub.K in the non-selection period, for which it holds that V.sub.K.C.sub.K =C.sub.I.V.sub.J. In other words, the value V.sub.J to be impressed is usually not reached and when the data remain the same, the pixel will have to be driven at least once at more the value V.sub.J, which leads to a delayed response.
Another source of error which leads to an erroneous first adjustment and hence a delayed response in a picture display device using active drive is the so-called DC offset voltage which occurs when using the drive mode in accordance with U.S. Pat. No. 5,032,83, but also when using other drive modes such as, for example, the drive mode using thin-film transistors.